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Need clarifation on testing temp. sending unit

bluexpy

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My '94 has some cooling issues - doesn't get hot, gauge doesn't read temp., coolant is rusty brown, etc.

I needed to verify if the coolant sending unit was working because the gauge did not report temp changes before I order a new one. I found the sending unit by the alternator and pulled the wire off. It was the same after shorting out. The temp. gauge moves very slightly when I turn the key on. It did the same before & after shorting out. So it's partially working. Maybe I pulled the wrong sending unit??

So exactly how does it need to be shorted out? Wire to negative battery post??

Thanks!
 



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wood1

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If it was my vehicle I would flush the cooling system and get it healthy. Look under BrooklynBay's useful threads for directions on flushing, I think it's called ten steps to a healthy cooling system, something like that anyway .

The guage sending unit is a one wire sender (I think) and if you ground the wire out on the engine the temp gauge should move. (Ignition on) If it doesn't move you have to figure out if it is the gauge itself, or the wiring to the gauge.

If you were interested in verifying the operation of the sender itself, you could hook a ohm meter to it and dunk it in water of different temperatures, measuring the resistance values, or gently heat it with a propane tourch.

Does your heater throw out any heat?
 






N7UBO

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91 XLT AND 94 Limited AND
Both the temp sending unit AND temp switch are located right behind the thermostat housing. Since they are potentially 14 years old, if they're original, I would just replace both. It's not that expensive...I just did the same with my limited. And by all means, flush the cooling system if the coolant is brownish. Your X will thank you in so many ways.
 






bluexpy

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That's what I plan to do. When I saw the coolant, I thought oil was in it! It was really rusty. At that point I knew I had to do a massive flush. I already bought a new thermostat and radiator cap.

I have that thread bookmarked. For future reference, it's here: http://www.explorerforum.com/forums/showthread.php?t=162848

While looking at the shelves today, saw some "super flush" additive. Are they helpful or harmful? Prestone sells one that is ideal for negelected cooling systems that fits my creitia.

Yes, my heater works. I haven't had gotten it fully warmed up, but all coolant hoses get warm after running a few minutes.

How do I ground out the sender wire? I want to verify if the dash gauge is functional or not. I'm not going to bother testing the sending unit, that will be replaced due to all the rust. BTW: Does Motorcraft still make the sending units? Rockauto only have the lousy overseas junk.
 






wood1

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When you pull the connector off the sensor and look into it, you'll see that there is only one connection and a nail or something similar will fit into it. Gently stick a small nail, or a piece of wire into it and let it rest against part of the engine that is a ground, the intake manifold right next to the sensor is a ground.

Switch on the ignition and have a look at the gauge, it should go full hot.

I would use a flush kit that ties into the heater hose as well as a flushing chemical, just be sure to flush the system well with clear water and get all the chemical out before you decide you're done and add antifreeze. I suggest you add Bar's Stop-Leak or something similar as it has anti-rust properties and a water pump lubricant in it as well.

I wouldn't replace any sensors unless you know they aren't working, rust in the coolant won't harm them.

You should have a very healthy cooling system after all that!
 






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